Liver Function Tests

Definition of Liver Function Tests (LFTs)

  • Liver Function Tests: Blood parameters indicating liver function or dysfunction.

  • Key enzymes include:

    • AST (Aspartate Transaminase)

    • ALT (Alanine Transaminase)

    • ALP (Alkaline Phosphatase)

    • GGT (Gamma-Glutamyl Transferase)

  • Key products include:

    • Albumin (protein produced by the liver)

    • Prothrombin Time (clotting factors produced by the liver)

    • Bilirubin (processed by the liver)

Reasons for Ordering LFTs

  • History of Liver Disease: Monitoring known conditions.

  • Symptoms: Such as jaundice (yellow discoloration) suggesting possible liver issues.

  • Medication Monitoring: Use of hepatotoxic drugs (e.g., paracetamol/acetaminophen).

  • Family History: Conditions like hemochromatosis affecting liver function.

  • High-Risk Groups Screening: Patients who had blood transfusions, viral hepatitis exposure, or drug use.

  • Extrahepatic Causes: Conditions like malignancy or hypoxia affecting liver function.

Understanding Jaundice and Bilirubin Levels

  • Jaundice: Yellow discoloration due to bilirubin accumulation.

    • Bilirubin levels above 1.2 mg/dL may indicate liver dysfunction.

  • Bilirubin Production:

    • Derived from breakdown of red blood cells, primarily in the spleen.

    • Unconjugated bilirubin is transported to the liver via albumin.

Liver Structure Relevant to LFTs

  • Liver Lobules: Functional units of the liver.

    • Composed of hepatocytes and blood supply from both portal vein and hepatic artery.

  • Functions of Hepatocytes:

    • Metabolize, filter blood, and produce bile.

    • Process bilirubin into conjugated (direct) bilirubin for excretion.

Causes of Elevated Bilirubin

  • Pre-Hepatic Causes: Increased red blood cell destruction (e.g., hemolytic anemia).

  • Intrahypatogenic Causes: Damage to liver cells leading to elevated bilirubin.

  • Post-Hepatic Causes: Issues with bile excretion leading to cholestasis.